1. Field of Art
This invention relates to method and apparatus used in connection with the handling of threaded tubulars. More particularly, this invention relates to method and apparatus used to position power makeup/breakout devices with respect to the end of a threaded connection half (of a threaded connection joining joints of tubular goods), in order that the power makeup/breakout device may either makeup (that is, screw together) or breakout (that is, unscrew) the threaded connection.
2. Related Art
Tubular goods manufactured in “joints,” typically on the order of 30 to 40 feet long, are commonly joined together to make up very long tubular strings, at times on the order of tens of thousands of feet long. While some tubular goods joints are welded together, commonly some sort of threaded connection is used, which permits the joints to be screwed together to form the tubular string, then unscrewed when needed.
Tubulars having threaded connections on either end are used in many industries, including but not limited to the oil and gas industry, borehole drilling, the drilling of pipeline crossing bores, and in a myriad of industrial settings such as chemical plants, manufacturing facilities, and the like. While the scope of the present invention is not restricted to any particular setting or use of tubulars having threaded connections, for illustrative purposes the following description will focus on tubulars used in the drilling of earthen boreholes for oil and gas wells, in particular drill pipe. Joints of drill pipe are usually joined by threaded connections commonly known as “tool joints.” The threaded connection is comprised of two halves: one half is the box, which contains the female threads, while the other half is the pin, containing the male threads. FIG. 1 shows a typical tool joint, not made up (that is, the pin not engaged in the box). The ends of the respective connection halves are also shown in FIG. 1. As can be seen in FIG. 1, an “upset” or larger outer diameter section is commonly present on both halves of the connection. The upset provides greater strength and provides a gripping surface for the tongs used to make up and breakout the connection. FIG. 1A shows the same threaded connection made up. The line at which the ends of the pin and box halves of the connection meet, for purposes of this application, is referred to as the “connection seam.” Similarly, a “connection end” is simply the end of a threaded connection, for example the end of the box connection, as shown in FIG. 1. For purposes of this application, the term “connection end” will encompass also the seam marking where two connection ends meet.
Traditionally, tool joints were made up and broken out with “manual” tongs, which hung from the rig derrick via cables and were swung into place onto the tool joint by the rig workers. The rig drawworks were then used to pull on the tongs (via cables), to makeup or break out the connection. Manual tongs are quite heavy, can be relatively slow to use, and require at least one rig worker for each tong (the “lead tong” and “backup tong”). For these and a variety of other reasons, including safety and efficiency reasons, combined power tong/backup units have come into common use on rigs to makeup and break out threaded connections. Power tong/backup units, while available in a variety of configurations, generally have a “power tong” section which has a set of powered rotary jaws, powered usually by hydraulic means, coupled to a “backup” section, which has hydraulic means to grip the connection and hold it stationary. The backup holds one side of the connection stationary, while the power tong turns the other side to makeup or break out as desired. For illustrative purposes, power tong/backup units and their use will be described for an arrangement with the power tong positioned over or above the backup. However, it is understood that an inverted arrangement is possible.
It is to be understood that the scope of the invention herein encompasses any sort of powered device to make up, and/or break out, threaded connections. For brevity, such devices (including the above-described power tong/backup units) may be referred to at times in this application as a “power tong unit.” Regardless of the configuration, it is readily appreciated that the power tong unit must be positioned so that one side of the power tong unit is grasping one side of the connection, while the other side of the power tong unit is grasping the other side of the connection end. The term “power tong unit” as used herein also encompasses the power tong half alone (that is, for example, used in conjunction with some sort of detached backup).
While power tong units can be suspended from the rig derrick by a cable, and swung into and out of engagement with the connection, powered positioning devices in various configurations have now come into use. Various configurations of such powered positioning devices comprising booms, rails, etc. are in use. Such positioning devices enable the operator to move power tong units horizontally into proper position to enable the tong jaws to grip the connection, and vertically into position with respect to the connection seam, with the power tong on one side of the seam and the backup on the other side. The operator moves the power tong unit into proper position by visually sighting the connection, particularly the connection seam. Obviously, the operator must stand relatively close to the connection to do so, and may have to contend with his line of sight being partially blocked by the power tong itself or other machinery.
For purposes of this application, the term “power positioner” is used at times to refer to any type or configuration of powered (whether by hydraulic or other means) device which at least partially positions a power tong unit on a connection.
This situation gives rise to the desirable goal of, at least partially, automating the positioning of the power tong on the connection. When manipulating threaded connections in rig operations, the position of the connection in a horizontal plane is always (within reasonably close tolerances) centered in the rotary drive of the rig. Therefore, automation of the horizontal element of power tong positioning is relatively easy.
However, the vertical position of the connection end with respect to the rig floor is a variable. The tubular is not set into the slips in the rotary table at a consistent height above the rotary table for every connection, therefore the position of the connection end above the rig floor will vary from connection to connection.
It can be readily appreciated that in order to automate tong positioning (that is, to position the tong on the connection with minimal human guidance) the height of the connection end with respect to some datum, for example above the rig floor, must first be determined, then that information must be input to a power positioner to vertically position the power tong unit along the longitude of the tubular (in addition to horizontal positioning).
Other applications have similar positioning needs. For example, in so-called “shop” environments, the power tong unit may be stationary and oriented to grasp substantially horizontally positioned tubulars; the tubular is placed horizontally, for example, on a powered roller. With this arrangement, rather than the power tong unit being moved with respect to stationary tubular, the power tong unit is stationary, and the tubular is moved by the roller so as to properly position the connection end with respect to the power tong.
Prior art methods and/or apparatus which have attempted to locate the connection end are believed to include mechanical devices such as feelers, and optical devices such as lasers. However, these prior art apparatus and methods are believed to exhibit various limitations on their use.
“Eddy Current” Techniques for Connection End Detection
It is known in the prior art to use so-called “eddy current” principles to detect discontinuities in the shape or structure of electrically conductive materials. For the present invention, eddy current principles are used to detect a “discontinuity” in electrically conductive tubulars, in the form of the connection end—whether the connection end marks the top or bottom of the tubular, as when only one of the connection halves is in place and the discontinuity is due to no material present past the connection end; or whether the connection end forms a connection seam, which, with respect to the tubular on either side of it, is a discontinuity, in that the seam marks where two separate pieces of electrically conductive material (metal) meet.
An alternating electric current, preferably a radio frequency alternating current, is flowed through at least one electric coil which is usually disposed in a housing and the resulting assembly commonly referred to in the art as a “probe.” An electro-magnetic field is thereby created around the probe. Impedance (generally, resistance to electric current flow), current, and phase angle can all be measured for the electric coil. These values can be measured, in a first or “undisturbed” state (that is, with unchanging presence of an electrically conductive object within the electro-magnetic field). Thereafter, an electrically conductive object (the object being examined to detect discontinuities therein) is moved within and relative to the electro-magnetic field, either by moving the electrically conductive object, or moving the coil. By principles well known to those in the relevant art, discontinuities in the electrically conductive object, for example, cracks, voids, or the like, both on and below the surface, can be detected by noting a change in the measured impedance, current or phase angle of current through the electric coil, as compared to the impedance when the discontinuity is not present within the magnetic field. The size and number of electric coils, geometry of the coils and/or housing, proximity of the electric coils to the object being tested, frequency of alternating current, voltage, etc. can be varied to accommodate particular applications, conditions to be investigated, etc. Inspection of various electrically conductive objects, especially metallic objects in the form of tubular goods, plates, fasteners, etc. may be carried out, to find discontinuities in the objects.
The present invention utilizes these principles in a novel method and apparatus for determining the position of a connection end on a tubular workpiece, to position power tongs on the threaded connection. A “discontinuity” in the form of the connection end is detected, and then the connection end and power tong unit (comprising a power tong alone, or combined power tong and backup) are properly positioned relative to one another, either by moving the power tong unit or the tubular or both.